From: John Sigler <linux.kernel@free.fr>
To: linux-kernel@vger.kernel.org,
linux-rt-users <linux-rt-users@vger.kernel.org>
Cc: johnstul@us.ibm.com, tglx@linutronix.de
Subject: Re: System clock frequency offset changes drastically across reboots
Date: Mon, 30 Jul 2007 09:59:48 +0200 [thread overview]
Message-ID: <46AD9A74.8070302@free.fr> (raw)
In-Reply-To: <46A9DD7A.80104@free.fr>
[ Expanding recipients list ]
John Sigler wrote:
> I'm using 2.6.20.7-rt8 on a P3.
But some ntpd users have reported the problem with mainline kernels and
different versions.
> I've noticed that the frequency offset of my system clock (computed
> either by ntpd, or by hand) changes drastically across reboots.
>
> By drastically, I mean +/- 60 ppm every time I reboot.
>
> Apparently this is caused by some imprecision in the frequency
> estimation done in calculate_cpu_khz() (arch/i386/kernel/tsc.c)
>
> My brutally crude work-around was to skip the computation altogether and
> hard-code the "correct" value for cpu_khz.
>
> http://linux.kernel.free.fr/cpu_khz.adlink
>
> Has this issue been investigated more thoroughly by other users?
Regards.
next prev parent reply other threads:[~2007-07-30 8:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-27 11:56 System clock frequency offset changes drastically across reboots John Sigler
2007-07-30 7:59 ` John Sigler [this message]
2007-08-03 7:47 ` John Sigler
-- strict thread matches above, loose matches on Subject: below --
2007-09-03 10:21 John Sigler
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